Combined AC-DC to DC converter

ABSTRACT

The invention relates to a combined AC-DC to DC converter. The converter provides the option of coupling to an AC supply source with at least one phase and the further option of coupling to at least one DC supply source. The converter obtains supply from at least one supply source at a time; and the converter contains controllable contact means that are, upon switching between supply sources, capable of connecting and disconnecting the individual supply sources to/from the converter; whereby a pulse signal is generated. The converter contains at least one coil that is in connection with at least one DC output. The proposed converter distinguishes itself over the prior art in that switching between supply sources is accomplished by means of the contact means over a period of time, where the pulse signal is divided into periods; and wherein the periods alternatingly originate from at least one first supply source and at least one second supply source; and wherein the current pulses from the first supply source is regulated in dependence on the current pulses from the second supply source; and wherein the converter contains means for voltage regulating at least one DC output. Hereby a flexible converter is obtained that can obtain supply from an AC supply source and one or more DC supply sources; and wherein switching between a first supply source and a second supply source can be accomplished without supply failures; and wherein, in overload situations, it is possible to draw on two or more supply sources.

CROSS-REFERENCE TO RELATED APPLICATION

This application is the National Stage of International Application No.PCT/DK02/0004, filed 22 Jan. 2002.

FIELD OF THE INVENTION

The invention relates to a combined AC-DC to DC-converter. The converterprovides at least one DC output from at least one AC supply with atleast one phase and at least one DC supply. The AC supply supplies an ACsignal comprising positive and negative half-periods. The convertercomprises at least one coil that is in connection with the DC output.The converter contains controllable contact means adapted for connectingand disconnecting the AC supply and the DC supply to and from theconverter.

BACKGROUND

Patent application No. WO 0033451 teaches a converter unit forconverting two or more DC voltage levels from the input of the converterunit to a DC voltage on the output of the converter unit, wherein theconverter unit comprises controllable switch means that are able toconnect and disconnect the individual DC input voltage level for formingan oscillating signal, and wherein the converter unit comprisesfiltering means for low pass filtering of the oscillating, signal forforming the DC voltage on the output of the converter unit.

The converter unit discussed in WO 0033451, however, presents aninconvenience because it cannot connect to an AC supply source.Additionally, the converter unit is not capable of performing a gradualswitch of supply source without supply loss, see the below descriptionof a method. Nor is the converter unit capable of performing an adaptiveswitch in case of overload situations.

U.S. Pat. No. 5,751,564 discloses a switching power supply system whichis able to connect two or more different power sources with differentvoltage levels, and can provide power even when the primary power sourceis low or completely absent. The output voltage is more constant than aconventional switching power supply, and the internal loss is alsosmaller. As a result, the back-up supply time is longer than that of aconventional UPS system. Finally, when used in a notebook computer, forexample, there is no need to use an AC to DC adapter when connecting toan AC power supply, it being possible to connect the switching powersupply directly to the AC power supply.

The ('564) system, however, is not capable of performing anuninterrupted switching between an AC supply source and a DC supplysource.

SUMMARY OF THE INVENTION

It is the object of the invention to provide a converter that can obtainsupply from one or more supply sources such as an AC source with one ormore phases in combination with one or more DC sources, whereinswitching from a first supply source to a second supply source isaccomplished gradually without supply failure; and wherein—in overloadsituations—it is possible to rely on one or more supply sources.

This can be accomplished in that the switching between supply sources isaccomplished by connecting and disconnecting the supply sources to/fromsaid converter based on phase information of the AC signal, whereby thesupply signal fed to said coil is divided into periods, wherein theperiods of the supply signal alternatingly originate from eitherpositive or negative half-periods of the AC signal and current pulsesfrom said DC supply; and wherein the current pulses from the DC supplyare regulated in dependence of the AC signal; and wherein the convertercontains means for voltage regulating said at least one DC output.

A flexible converter is achieved that can obtain supply from an ACsupply source and one or more DC supply sources; and wherein switchingfrom a first supply source to a second supply source can be accomplishedwithout supply loss; and wherein—in overload situations—two or moresupply sources can be relied on. In a typical overload situation with anAC source in the form of a current network from a diesel generator and aDC source in the form of a battery, the advantage of this converter isthat the current from the AC source can be maintained on a constanthighest value in that supplementary energy is supplied from the DCsource. It is possible to use smaller cables and fuses in the AC sourcewithout such fuses being blown upon overload.

The term ‘supply source’ is used herein to designate either an AC sourcewith one or more phases connected via a common point of reference, or aDC source or two DC sources that are connected in series via a commonpoint of reference, whereby a positive and a negative supply voltage areobtained.

The converter is characterized in that the AC supply source is asingle-phase AC source and that at least one DC source is provided. Aconverter for single-phase systems is obtained that protects againstsupply failures in case of abrupt switching between the single-phase ACsupply source and one, optionally more, DC sources.

The converter is characterized in that the AC supply source is apolyphase AC source and that at least one DC source is provided. Aconverter for polyphase systems is obtained that protects against supplyfailures in case of abrupt switching between the polyphase AC supplysource and one, optionally more, DC sources.

The converter is characterized in that, on the basis of a signal from acurrent detector that measures the current through a coil, a controlcircuit has means for connecting and disconnecting, respectively, theone terminal of the coil to/from a DC supply source; and means toconnect and disconnect, respectively, the second terminal of the coilto/from a common point of reference. The current through the coil flowsto the DC output of the converter during periods when the secondterminal of the coil is not connected to the common point of reference.The converter is provided with means for connecting and disconnecting,respectively, an AC supply source to the one terminal of the coil, iethat terminal on the coil that can also be connected to the DC source. Aconverter is obtained that has the smallest possible number ofcomponents and that is simultaneously capable of performing a gradualswitch between supply sources; wherein the one supply source is an ACsupply source; and the second supply source is a DC supply source. Theconverter protects against supply failures during abrupt switchesbetween supply sources.

The converter is characterized in that at least one converter is used toform a DC output that is positive relative to a common point ofreference; and at least one converter is used to form a DC output thatis negative relative to a common point of reference. A converter isobtained that is able to deliver a positive, optionally more positive,DC output voltages, and one negative, optionally more negative DC outputvoltages that are protected against supply failures during abruptswitches between supply sources.

The converter is characterized in that the AC supply source is sharedfor the converters that are used to form a positive output voltage andthe converters that are used to form a negative output voltage relativeto a common point of reference. A converter is obtained that makesrequirements to the smallest possible number of AC supply sources. Thisis a major advantage in that, thus, the converter can also be used wherethe availability of AC supply sources is scarce.

The converter is characterized in that the means for connecting anddisconnecting, respectively, the one terminal of the coil to/from a DCsupply source is a controllable switch. The controllable switch can beregulated to be connected for-at least a part of every otherhalf-period. It is possible to regulate the period of time when supplyis obtained from the DC supply source. This is associated with theadvantage that it enables parallel coupling of a number of converters tothe same battery. Each converter is then allocated a period of time thatis different from that of the other converters, during which theconverters obtain energy exclusively from the DC supply source. Theoption of parallel coupling converters to the same DC supply source alsomeans that supply can be obtained by using as few DC sources aspossible.

The converter is characterized in that the means for connecting anddisconnecting, respectively, the second terminal of the coil to/from acommon point of reference is a controllable switch. The controllableswitch can be regulated to be connected for at least a part of everyother half-period, and the controllable switch is typically connected inburst series. It is possible to regulate the voltage through the coil.On the one hand it makes it possible to perform a gradual switching inconsumption of energy from the DC source, and on the other hand it makesit possible to adjust the nominal output voltage on the converter withina field. The option of adjusting the nominal output voltage of theconverter within a field means that the same converter design can beused where there is a requirement for several different output voltages.Thereby the number of different converters can be reduced.

The converter is characterized in that semi-conducters are used ascontrollable switches comprising at least one of the types of fieldeffect transistor, bipolar transistor, insulated Gate Bipolar Transistor(IGBT), Gate Turn-Off Tyristor (GTO) and Injection Enhanced GateTransistor (IEGT). It is possible to select semi-conductor technologywhile taking into consideration requirements to supply, construction andspace.The converter is characterized in that—in an overload situation—thecurrent from the AC supply source is limited to a constant largestvalue, in that supplementary energy is supplied from the DC supplysource.A gentle load of the AC support source is obtained, wherein theconverter does not expose the AC supply source to overload.

BRIEF DESCRIPTION OF THE FIGURES

The invention will now be described in further detail with reference tothe accompanying figures, wherein

FIG. 1 shows a single-phase combined AC-DC to DC converter with positiveas well as negative output voltage; and

FIG. 2 shows curves of a ramp-in course for a single-phase combinedAC-DC to DC converter with positive as well as negative output voltage;and

FIG. 3 shows a single-phase combined AC-DC to DC converter with positiveoutput voltage; and

FIG. 4 shows curves of a ramp-in course for a three-phase combined AC-DCto DC converter with positive as well as negative output voltage; and

FIG. 5 shows curves of an overload course for a single-phase combinedAC-DC to DC converter with positive as well as negative output voltage;and

FIG. 6 shows curves of an overload course for a three-phase combinedAC-DC to DC converter with positive as well as negative output voltage;and

FIG. 7 shows a three-phase combined AC-DC to DC converter with positiveas well as negative output voltage constructed from three converterswith shared DC supply; and

FIG. 8 shows a three-phase combined AC-DC to Dc converter with positiveoutput voltage constructed from three converters with shared DC supply.

DETAILED DESCRIPTION

FIG. 1 shows a single-phase combined AC-DC to DC converter 100 withpositive as well as negative output voltage. The positive terminal on abattery 101 is connected to the anode on a tyristor 106. The negativeterminal on the battery 101 is connected to a common point of reference104. The cathode on the tyristor 106 is connected to the cathode on adiode 119. The gate on the tyristor 106 is connected to an output on acontrol circuit 108. The cathode on the tyristor 106 is connected to acoil 112. A current sensor 114 encloses the connection between thetyristor 106 and the coil 112. The current sensor 114 is connected to aninput on the control circuit 108. The coil 112 is further connected tocollector on a transistor 110. Collector on the transistor 110 isconnected to the anode on a diode 121. Emitter on the transistor 110 isconnected to the common point of reference 104. An output on the controlcircuit 108 is connected to the base of the transistor 110. The cathodeon the diode 121 is connected to a capacitor 123 and to a DC output 125.The capacitor 123 is further connected to the common point of reference104. The DC output 125 is connected to the control circuit 108. Thenegative terminal on a battery 102 is connected to the cathode on atyristor 107. The positive terminal on the battery 102 is connected tothe common point of reference 104. The anode on the tyristor 107 isconnected to the anode on a diode 120. The gate on the tyristor 107 isconnected to an output on a control circuit 109. The anode on thetyristor 107 is connected to a coil 113. A current sensor 115 enclosesthe connection between the tyristor 107 and the coil 113. The currentsensor 115 is connected to an input on the control circuit 109. The coil113 is further connected to emitter on a transistor 111. Emitter on thetransistor 111 is connected to the cathode on a diode 122. Collector onthe transistor 111 is connected to the common point of reference 104. Anoutput on the control circuit 109 is connected to the base of thetransistor 111. The anode on the diode 122 is connected to a capacitor124 and to a DC output 126. The capacitor is further connected to thecommon point of reference 104. The DC output 126 is connected to thecontrol circuit 109. The anode on the diode 119 is connected to a node118. The cathode on the diode 120 is connected to the node 118. The node118 is connected to a switch 127. The switch 127 is further connected toa single-phase AC source 103 and to the input of a synchronizing circuit105. The single-phase AC source 103 is further connected to the commonpoint of reference 104. The first output of the synchronizing circuit105 is connected to an input on the control circuit 108, and the secondoutput of the synchronizing circuit 105 is connected to an input on thecontrol circuit 109, and the third output of the synchronizing circuit105 is connected to a control input on the switch 127.

It is the task of the synchronizing circuit 105 to register when the ACsource 103 is present with a valid voltage with a view to connecting theAC source 102 to the converter 100 via the switch 127. Besides, thesynchronizing circuit 105 serves the purpose of synchronizing to the ACsupply by generating synchronous control signals to the control circuits108, 109 with a known phase relative to the AC supply. In the positivehalf-period of the single-phase AC source 103, the current flows fromthe single-phase AC-source 103 through the contact 127, further throughthe diode 119, and further through the coil 112. If the transistor 110is interrupted, the current flows from the coil 112 further through thediode 121 to the DC output 125, and if the transistor 110 is connected,the current flows from the coil 112 to the common point of reference104. The tyristor 106 is disconnected for this period. In the negativehalf-period of the single-phase AC source 103, the control circuit 108switches on the tyristor 106, whereby the current from the battery 101flows through the tyristor 106 and further through the coil 112. If thetransistor 110 is interrupted, the current flows from the coil 112 tothe DC output 125, and if the transistor 110 is connected, the currentflows from the coil 112 to the common point of reference 104. Thecontrol circuit 108 controls the transistor 110 with pulses of varyingduty-cycle, and at a frequency that is usually considerably moreelevated than the frequency of the single-phase AC source 103. Theauxiliary circuit consisting of the coil 112, the transistor 110 and thediode 121 constitutes a boost converter. During periods when thetransistor 110 is connected the current increases in the coil 112.During periods when the transistor is disconnected, the current flows onthrough the diode 121 to the DC output 125 and will simultaneously startto decrease, the voltage above the coil 112 now having opposite polaritysign. Regulation of the duty-cycle for the transistor 110 enablesregulation of the current in the coil 112 and thus also the voltage onthe DC output 125. The valid duty cycle for the transistor 110 isdetermined by the control circuit 108 on the basis of the output voltagethat is measured via a return coupling from the DC output 125. Thecapacitor 123 smoothens the voltage on the DC output 125 to a DCvoltage. In the negative half-period of the single-phase AC source 103,the current flows to the single-phase AC-source 103 from the switch 127,further from the diode 120, and further from the coil 113. If thetransistor 111 is disconnected, the current flows to the coil 113further from the diode 122 from the DC output 126, and in case thetransistor 111 is connected, the current flows to the coil 113 from thecommon point of reference 104. The tyristor 107 is, for this period oftime, disconnected. In the positive half-period of the single-phase ACsource 103, the control circuit 109 switches on the tyristor 107,whereby the current to the battery 102 is caused to flow from thetyristor 107 and on from the coil 113. If the transistor 111 isdisconnected, the current flows to the coil 113, from the diode 122,from the DC output, and if the transistor 111 is connected, the currentflows to the coil 113 from the common point of reference 104. Thecontrol circuit 109 controls the transistor 111 with pulses of varyingduty-cycle and at a frequency that is usually considerably more elevatedthan the frequency of the single-phase AC source 103. The auxiliarycircuit consisting of the coil 113, the transistor 111, and the diode122 constitutes a boost converter. During periods when the transistor111 is connected, the current increases in the coil 113. In periods whenthe transistor 111 is disconnected, the current flows on from the diode122 from the DC output 126 and will simultaneously start to decrease,the voltage above the coil 113 now having opposite polarity sign.Regulation of the duty cycle for the transistor 111 enables regulationof the current in the coil 113 and thus the voltage on the DC output126, too. The valid duty-cycle for the transistor 111 is determined bythe control circuit 109 on the basis of the out-put voltage that ismeasured via a return coupling from the DC output 126.

The capacitor 124 smooths the voltage on the DC output 126 to a DCvoltage. The regulation consists of two independent regulation systems,one for the positive output voltage in the control circuit 108 andanother for the negative output voltage in the control circuit 109. Eachof these regulation systems has the object of maintaining a constantoutput voltage and simultaneously absorbing a current with apredetermined well-defined curve shape, whether the current comes fromthe AC source or the DC source. This is accomplished in practice byusing for each of the two control circuits 108 and 109 two regulatorloops, one that maintains the curve-shape on the current, and anotherwhose task it is to maintain the constant output voltage. The regulatorloop that determines the current curve shape will usually be the fastestof the two regulator loops. It emits on the output a pulse-widthmodulated signal to one of the two transistors 110 or 111. Each time thetransistor 110, 111 is switched on, the current in the coil 112, 113will increase.

Each time it is switched off, the current will decrease, the voltageabove the coil 112, 113 having in that case the opposite polarity sign.In practice this current control can be performed in accordance withvarious principles that either keep a constant or variable frequency, orcontrol in accordance with the instantaneous or average value of thecurrent, averaged over several pulses. These various principles must beconsidered to be prior art and all are able to control the current inthe coil 112, 113 of a converter 100 to follow optimally the amplitudeand the curve-shape on a supplied signal. This is accomplished bycomparing the measured value of the current to a signal that correspondsto the desired voltage and continuously adapting the pulse/break-ratio:The current in the coil 112, 113 will all the time either increase ordecrease, but is regulated continuously with the pulse/break-ratio, suchthat—averaged over several pulses—it corresponds to the desiredcurve-shape. The term ‘pulses’ as used in this context is intended todesignate control pulses for the transistor 110, 111 that will normallybe an elevated frequency compared to the current network frequency. Thisregulator loop receives a signal with a curve-shape and amplitude thatcorresponds to the current that it is desired that the relevantconverter 100 shall draw at a given time. This curve-shape issubsequently referred to as the current reference. The curve-shape ofthis of the current reference depends on the operating mode of theconverter 100. When it is desired to draw current from the AC source 103only, the curve-shaped will be positive and negative half-periods,respectively, of a sinusoidal signal, such that the total amount ofcurrent that is drawn from the net will become sinusoidal. This is thecurve-shape that is seen as curve 231 in FIG. 1 during the time 236.When it is desired to draw current from the battery 101, 102 only, thereference to both halves of the converter 100 will exclusively be DCsignals, since—in that case—it is desired to draw a constant DC currentfrom the battery 101, 102. When it is desired to draw current from bothsources, the current reference will have an appearance that correspondsto the curve 231 in FIG. 2 during the time 235. This curve-shapeconsists partly of sinusoidal half-waves and partly of rectangular ortrapezoidal pulses. The current reference described can either begenerated as a voltage or current curve-shape of an electronic circuit,or it can be a digitally computed curve-shape, generated by, e.g., amicroprocessor or a Digital Signal Processor (DSP). In order to know inwhich of the described operation forms, the run is performed, a detectorcircuit 105 is present that decides whether the AC source 103 is presentand has an acceptable voltage quality. When this has been complied with,AC operation is selected. If the AC source 103 disappears or is in anyother way detected to be unacceptable as to either voltage or frequency,switching is performed to battery-operation. When the AC voltage isagain present and acceptable, a ramp-in course is made, line in FIG. 2.The detector circuit 105 can be shared by both converters. In order togenerate the desired curve shapes, a synchronization unit 105 is alsoused. It also receives the AC signal and synchronizes to this AC signal.It is thereby able to emit phase information to the twocontrol/regulator units 109 and 109 that tells where in time one isrelative to the zero transit on the AC signal, e.g., as a degree figurebetween zero and 360 degrees. Such phase information is subsequentlyused to determine the course in time of the described curve-shapes. Inaddition to said signals concerning operating mode and synchronization,it must also be possible to continuously adapt the amplitude on thedescribed current references. By changing the amplitude on the signals,the amount of current to be drawn from the AC source 103 or the DCsource 101, 102 is changed, and thus how much power is supplied to theconverter 100. This power supply must continuously be adapted to exactlycover the need for power that is drawn from the converter 100 output(s)plus what can be ascribed to loss. In case more power is supplied thanneeded, it would mean that the voltage on the capacitors 123 or 124 willcontinue to increase, and correspondingly the voltages will decrease iftoo little power is supplied. In order to thereby maintain the correctoutput voltage there is therefore in each of the control/regulatorcircuits 108 and 109 a regulator loop that measures the voltages on 125and 126 and compares them to suitable reference values. In case theoutput voltage deviates from the desired, the amplitudes on thedescribed current reference signals are regulated upwards or downwards.Only one specific maximum value for the current drawn from the AC source103 is allowed at all times. During a ramp-in course, this maximum valueis increased linearly from zero to a predetermined maximum value withina predetermined period, e.g., 10 seconds. If it is desired to supplymore current or power than allowed by this maximum value, there isformed, on the one hand, half-wave shaped sinusoidal signals with themaximally allowed value, whereas the remainder of the power need iscovered by current pulses from the battery. The distribution between thetwo pulses is calculated continuously, such that they combine to coverthe need for supplied power. Correspondingly, this limitation of ACcurrent pulses is used to delimit the current from a current network ordiesel generator during overload. Also in this case it is calculated howmuch supplement is needed from the battery to deliver the requisitetotal amount of power. if the node 118 is split and if the AC source 103and the switch 127 are connected instead to the alternating currentinputs of a rectifier bridge, where the positive output of the rectifierbridge is connected to the anode on the diode 119, and the negativeoutput of the rectifier bridge is connected to the cathode on the diode120, it is also possible to obtain supply from the AC source 103 in bothhalf-periods to both the positive half and the negative half of theconverter 100. Hereby the power consumption from the batteries 101; 102can be reduced.

FIG. 2 shows curves of a ramp-in course for a single-phase combinedAC-DC to DC converter 100 with positive as well as negative outputvoltage. A first curve 231 shows the current through the coil 112. Asecond curve 232 shows the current through the coil 113. A third curve233 shows the total current of the single-phase AC source 103. To thefirst curve 231, and the second curve 232 and the third curve 233 itapplies that a first period of time 234 shows supply exclusively fromthe batteries 101, 102 and a second period of time 235 shows a ramp-incourse with supply from the batteries 101, 102 and the single-phase ACsource 103, where the current from the batteries 101, 102 is reduced inpace with the current from the single-phase AC current 103 beingincreased, and further a third period of time 236 that shows supplyexclusively from the single-phase AC source 103.

During the period of time 234, the batteries 101, 102 supply alone thecombined AC-DC to DC converter 100. During the period 235 a ramp-incourse takes place, where supply is accomplished from the batteries 101,102 as well as from the single-phase AC source 103. The strength of thepulse current from the batteries 101, 102 is reduced in pace with thepulse current from the single-phase AC source 103 being increased.During the period of time 236 the single-phase AC source 103 deliversexclusively to the combined AC-DC to DC converter 100.

FIG. 3 shows a single-phase combined AC-DC to DC converter 300 withpositive output voltage. The positive terminal on a battery 301 isconnected to the anode on a tyristor 306. The negative terminal on thebattery 301 is connected to the anode on a tyristor 306. The negativeterminal on the battery 301 is connected to a common point of reference304. The cathode on the tyristor 306 is connected to the cathode on adiode 319. The gate on the tyristor 306 is connected to an output on acontrol circuit 308. The cathode on the tyristor 306 is connected to acoil 312. A current sensor 314 encloses the connection between thetyristor 306 and the coil 312. The current sensor 314 is connected to aninput on the control circuit 308. The coil 312 is further connected to acollector on a transistor 310. Collector on the transistor 310 isconnected to the anode on a diode 321. Emitter on the transistor 310 isconnected to the common point of reference 304. An output on the controlcircuit 308 is connected to the base of the transistor 310. The cathodeon the diode 321 is connected to a capacitor 323 and to a DC output 325.The capacitor 323 is further connected to the common reference point304. The DC output 325 is connected to the control circuit 308. Theanode on the diode 319 is further connected to switch 327. The switch327 is further connected to a single-phase AC source 303 and to theinput of a synchronization circuit 305. The single-phase AC source 303is further connected to the common reference point 304. The one outputof the synchronization circuit 305 is connected to an input on thecontrol circuit 308, and the second output of the synchronizationcircuit 305 is connected to a control input on the switch 327.

The indication of functionality for a single-phase combined AC-DC to DCconverter 300 with positive output voltage, in accordance with FIG. 3,follows the indication of functionality for the positive half of asingle-phase combined AC-DC to DC converter 100 with positive as well asnegative output voltage, in accordance with FIG. 1. Like thesingle-phase combined AC-DC to DC converter 100 with positive as well asnegative output voltage, the AC source 303 and the switch 327 caninstead be coupled to the alternating-current inputs of a rectifierbridge, where the positive output of the rectifier bridge is connectedto the anode on the diode 319, and the negative output of the rectifierbridge is connected to the reference point 304. Hereby it is possible toobtain supply from the AC source 303 in both half-periods to theconverter 300. Hereby the power consumption from the battery 301 can bereduced.

FIG. 4 shows curves of a ramp-in course for a three-phase combined AC-DCto DC converter 700, 740, 780 with positive as well as negative outputvoltage. A first curve 431 shows the current through the coil in thepositive half of the converter for a phase (phase 1). A second curve 432shows the current through the coil in the negative half of the converterfor the same phase (phase 1). A third curve 433 shows the total amountof current of the AC source 703 for the same phase (phase 1). A fourthcurve 437 shows the total amount of current from the battery 701 to thepositive half of the converter for all three phases (phase 1, phase 2and phase 3). A fifth curve 438 shows the total amount of current to thebattery 702 from the negative half of the converter for all three phases(phase 1, phase 2 and phase 3). To the first curve 431, and the secondcurve 432, and the third curve 433, and the fourth curve 437, as well asthe fifth curve 438 it applies that a first period of time 434 showssupply exclusively from the batteries 701, 102, and a second period oftime 435 shows a ramp-in course with supply from the batteries 701, 702and the AC source 703, where the current from the batteries 701, 702 isreduced in pace with the current from the AC source 703 being increased,and also a third period of time 436 that shows supply exclusively fromthe AC source 703.

The indication of functionality for the ramp-in course for a three-phasecombined AC-DC to DC converter 700, 740, 780 with positive as well asnegative output voltage, in accordance with FIG. 4, follows theindication of functionality for the ramp-in course for a single-phasecombined AC-DC to DC converter 100 with positive as well as negativeoutput voltage, in accordance with FIG. 2. It is noted that thebatteries 701, 702 are shared (and identical) for converters 700, 740,780 for all three phases (phase 1, phase 2 and phase 3). Batteries 701,702 deliver to three otherwise independent circuits 700, 740, 780 thateach corresponds to a single-phase combined AC-DC to DC converter 100with positive as well as negative output voltage, in accordance withFIG. 1. This means that the battery 701 is connected to three tyristorsin each their circuit 700, 740, 780, and the battery 702 is connected tothree tyristors in each of the same three circuits. The three circuits700, 740, 780 use each their phase, where the common point of reference704 is shared for the three phases.

FIG. 5 shows curves of an overload course for a single-phase combinedAC-DC to DC converter 100 with positive as well as negative outputvoltage. A first curve 539 shows the current load in percentagesrelative to an allowable upper current threshold. A second curve 531shows the current through the coil 112. A third curve 532 shows thecurrent through the coil 113. A fourth curve 533 shows the total amountof current of the single-phase AC source 103. To the first curve 539,and the second curve 531, and the third curve 532, and the fourth curve533 it applies that a first and third period of time 536 show normaloperation with supply exclusively from the single-phase AC source 103,and a second period of time 540 shows an overload course with supplyfrom both the batteries 101, 102 and the single-phase AC source 103,where the current from the batteries 101, 102 are of such magnitude thatthe current from the single-phase AC source 103 is kept constant andalso within certain allowable current thresholds.

During the two periods 536 normal operations take place, where thesingle-phase AC source 103 alone delivers to the combined AC-DC to DCconverter 100. During the period of time 540 an overload course occurs,where supply takes place from both the batteries 101, 102 and thesingle-phase AC source 103. The pulse current from the batteries 101,102 is adjusted to such magnitude that compensation is fully made forthe overload, whereby the current from the single-phase AC source 103 iskept constant and within certain allowable thresholds.

FIG. 6 shows curves of an overload course for a three-phase combinedAC-DC to DC converter 700, 740, 780 with positive as well as negativeoutput voltage. A first curve 639 shows the current load as percentageson all three phases relative to an allowable upper current threshold. Asecond curve 631 shows the current through the coil in the positive halfof the converter for a phase (phase 1). A third curve 632 shows thecurrent through the coil in the negative half of the converter for samephase (phase 1). A fourth curve 633 shows the total amount of current ofthe AC source 703 for the same phase (phase 1). A fifth curve 637 showsthe total amount of current from the battery 701 to the positive half ofthe converter to all three phases (phase 1, phase 2 and phase 3). Asixth curve 638 shows the total amount of current to the battery 702from the negative half of the converter from all three phases (phase 1,phase 2 and phase 3). To the first curve 639, and the second curve 631,and the third curve 632, and the fourth curve 633 it applies that afirst and third period of time 636 show normal operation with supplyexclusively from the AC source 703, and a second period of time 640 thatshows an overload course with supply from both the batteries 701, 702and the AC source 703, where the current from the batteries 701, 702 isof such magnitude that the current from the AC source 703 is keptconstant and further within given allowable current thresholds.

The indication of functionality for the overload course for athree-phase combined AC-DC to DC converter 700, 740, 780 with positiveas well as negative output power, in accordance with FIG. 6, follows theindication of functionality for the overload course for a single-phasecombined AC-DC to DC converter 100 with positive as well as negativeoutput load, in accordance with FIG. 5. It is noted that the batteries701, 702 are shared (and identical) for converters 700, 740, 780 for allthree phases (phase 1, phase 2 and phase 3). Batteries 701, 702 deliverto three otherwise independent circuits 700, 740, 780, that eachcorresponds to a single-phase combined AC-DC to DC converter 100 withpositive as well as negative output voltage, in accordance with FIG. 1.This means that the battery 701 is connected to three tyristors in eachtheir circuit 700, 740, 780 and the battery 702 is connected to threetyristors in each of the same three circuits. The three circuits 700,740, 7809 use each their phase, wherein the common point of reference704 is shared for the three phases.

FIG. 7 shows a three-phase combined AC-DC to DC converter with positiveas well as negative output voltage constructed by means of threeconverters 700, 740, 80 with shared DC supply 701, 702. The positiveterminal on a battery 701 is connected to the anode on a tyristor ineach of the three converters 700, 740, 780 corresponding to the tyristor106 in FIG. 1. The negative terminal on the battery 701 is connected toa common point of reference 704. The negative terminal on a battery 702is connected to the cathode on a tyristor in each of the threeconverters 700, 740, 780, corresponding to the tyristor 107 in FIG. 1.The positive terminal on the battery 702 is connected to the commonpoint of reference 704. A switch in each of the three converters 700,740, 780, corresponding to the switch 127 in FIG. 1, is connected toeach their phase on an AC source 703. The AC source 703 is furtherconnected to a common point of reference 704. The positive outputs ofthe three converters 700, 740, 780 are all connected to an output 725.The negative outputs of the three converters 700, 740, 780 are allconnected to an output 726. The references of the three converters 700,740, 780 are all connected to the point of reference 704.

The indication of functionality for a three-phase combined AC-DC to DCconverter with positive as well as negative output voltage constructedfrom three converters 700, 740, 780 with shared DC supply 701, 702, inaccordance with FIG. 7, follows the indication of functionality for asingle-phase combined AC-DC to DC converter 100 with positive as well asnegative output voltage, in accordance with FIG. 1.

FIG. 8 shows a three-phase combined AC-DC to DC converter with positiveoutput voltage constructed from three converters 800, 840, 880 withshared DC supply 801. The positive terminal on a battery 801 isconnected to the anode on a tyristor in each of the three converters800, 840, 880, corresponding to the tyristor 306 in FIG. 3. The negativeterminal on the battery 801 is connected to a common point of reference804. A switch in each of the tree converters 800, 840, 880,corresponding to the switch 327 in FIG. 3, is connected to each theirphase on an AC source 803. The AC source 803 is further connected to acommon point of reference 804. The negative outputs of the threeconverters 800, 840, 880 are all connected to an output 825. Thereferences of the three converters 800, 840, 880 are all connected tothe point of reference 804.

The indication of functionality for a three-phase combined AC-DC to DCconverter with positive as well as negative output voltage constructedfrom three converters 800, 840, 880 with common DC supply 801, inaccordance with FIG. 8, follows the indication of functionality for thepositive half of a single-phase combined AC-DC to DC converter 100 withpositive as well as negative output voltage, in accordance with FIG. 1.

The converter (100, 300, 700, 740, 780, 800, 840, 880) can becharacterized, e.g., in that—at a given load, typically full load—on atleast one DC output (125, 126, 325, 725, 726, 825) switches occuradaptively from a DC supply source (101, 102, 301, 701, 702, 801) to anAC supply source (103, 303, 703, 803), typically a diesel generator,while taking into consideration stability of frequency and voltage onthe AC supply source (103, 303, 703, 803). By such adaptive switch ofsource, gradual switching from the DC supply source to the AC supplysource will occur, where supply from both supply sources takes placeduring the switching time. The adaptive switch of source optionallycomprises that there are several, consecutive periods with supply fromboth supply sources. Finally, the adaptive switching of source meansthat it is possible to switch completely or partially back to the DCsupply source. Hereby a gentler coupling onto the AC supply source isobtained, where the converter does not expose the AC supply source toabrupt and forceful loading couplings. Hereby the AC source is protectedagainst overload with ensuing fluctuation of, e.g., frequency andvoltage. If the AC source is, e.g., a diesel generator, it is importantto avoid abrupt and forceful loading couplings, since they translateonto the rotor current, whereby the diesel generator becomes instablewith regard to both frequency and voltage. In a worst-case scenario, theinstability may result in self-oscillation with ensuing supply failures.

The converter (100, 300, 700, 740, 780, 800, 840, 880) can be, e.g.,characterized in that—upon supply from an AC supply source (103, 303,703, 803), typically a diesel generator, dynamic load changes arecompensated, where the current from at least one DC output (125, 126,325, 725, 726, 825) is increased adaptively. The adaptive compensationof dynamic load changes occurs with due regard to stability of frequencyand voltage on the AC supply source (103, 303, 703, 803) by obtainingsupplementary energy from a DC supply source (101, 102; 301, 701, 702,801). By such adaptive compensation of dynamic load changes, asupplementary supply from the DC supply source will occur, in thatsupply will—for a period of time—take place from both supply sources.Optionally there may be several consecutive periods with supply fromboth supply sources. Hereby a gentler load onto the AC supply source isobtained, where the converter does not expose the AC supply source toabrupt and forceful loading couplings. Hereby the AC source is protectedagainst overload with ensuing fluctuation of, e.g., frequency andvoltage. If the AC source is, e.g., a diesel generator, it is importantto avoid abrupt and forceful loading couplings, since they translateonto the rotor current.

Hereby the diesel generator becomes instable with regard to bothfrequency and voltage, and in a worst-case scenario, the instability mayresult in self-oscillation with ensuing supply failures.

1. A converter for providing at least one DC output from at least one ACsupply with at least one phase and at least one DC supply, the at leastone AC supply supplying an AC signal comprising positive and negativehalf-periods, the converter comprises at least one coil that is inconnection with the at least one DC output, the converter containscontrollable contact means for connecting and disconnecting the at leastone AC supply and the at least one DC supply to/from said converterwherein connecting and disconnecting of the AC and DC supplies to/fromsaid converter is based on phase information of the AC signal, wherebythe AC signal fed to the coil is divided into periods, wherein theperiods of the AC signal alternatingly originate from either positive ornegative half-periods of the AC signal and current pulses from the atleast one DC supply; and wherein the current pulses from the at leastone DC supply are regulated in dependence of the AC signal; and whereinthe converter contains means for voltage regulating the at least one DCoutput.
 2. A converter according to claim 1, wherein the at least one ACsupply source is a single-phase AC source.
 3. A converter according toclaim 1, wherein the at least one AC supply source is a poly-phase ACsource.
 4. A converter according to claim 1, wherein—on the basis of asignal from a current detector that measures the current through a firstcoil of the at least one coil, a control circuit has means forselectively connecting a second terminal of the first coil to a first DCsupply of the at least one DC supply, and to a common point ofreference; and that the current through the first coil flows to a firstDC output of the at least one DC output of the converter during periodsof time, where the second terminal of the first coil is not connected tothe common point of reference; and that the converter has means forconnecting and disconnecting, respectively, a first AC supply of the atleast one AC supply source to/from the second terminal of the firstcoil.
 5. A converter according to claim 1, wherein at least oneconverter is used to form a positive DC output relative to a commonpoint of reference; and at least one converter is used to form anegative DC output relative to a common point of reference.
 6. Aconverter according to claim 5, wherein the at least one AC supplysource is shared by the at least one converters that is/are used to formthe positive DC output voltage and the at least one converters thatis/are used to form the negative DC output voltage, respectively,relative to a common point of reference.
 7. A converter according toclaim 4, wherein the means for selectively connecting includes acontrollable switch; and that the controllable switch can be regulatedto be connected for at least a part of every other half-period.
 8. Aconverter according to claim 4, wherein the means for selectivelyconnecting includes a controllable switch; and that the controllableswitch can be regulated to be connected for at least a part of everyother half-period; and that the controllable switch is typicallyconnected in burst series.
 9. A converter according to claim 4, whereinthe means for selectively connecting includes semiconductors used ascontrollable switches comprising at least one of a field powertransistor, bipolar transistor, Insulated Gate Bipolar Transistor(IGBT), Gate Turn-Off Tyristor (GTO) and Injection Enhanced GateTransistor (IEGT).
 10. A converter according to claim 1, wherein, in anoverload situation, the current from the at least one AC supply sourceis limited to a constant maximum value, in that supplemental energy issupplied by the at least one DC supply source.